There are many types of machines that employ high-intensity radiation sources, wherein the radiation and the associated heat need to be controlled. For example, many types of projectors, including overhead projectors, slide projectors, television projectors, and movie projectors utilize high intensity light sources in order to provide sufficient light energy to illuminate a remote surface with a magnified and projected image from a small image source. Computer addressable projection systems have become available in recent years, whereby a computer generated image may be projected onto a wall or screen. These originally took the form of a projection TV system or an LCD panel that could be placed on an overhead projector. The overhead projector provided the light source and optics to project the computer-generated image from the LCD panel. So-called "integrated projectors" are now available, which provide a complete projection system for computer-generated images. The video output of a computer can be connected directly to an integrated projector, which is typically a compact unit including a light source, power supply, LCD panel, optical elements, and the required electronics.
Typical light sources used in video projector systems can usefully employ light energy only in visible wavelengths, between about 400 and 700 nanometers, for example, but they also generate large quantities of light energy in the near infrared wavelengths, roughly between about 780 and 2500 nanometers. This infrared radiation heats the objects that are exposed to it, and the heat must be dissipated without allowing the temperature of components in the projector to rise to harmful levels. Most projectors are designed to capture the infrared radiation from the light source, convert it to heat, and exhaust the heat from the projector using a forced air ventilation system.
Integrated projectors have presented a number of new challenges to the engineers who design them. They are expected to be compact and light weight, for they are often transported by their users in conjunction with portable computers. At the same time, they require higher intensity light sources than are typically used with slide projectors and overhead projectors, because of the higher optical density and higher resolution of the LCD panels, the higher level of image magnification that is desired, and because they are often used in relatively high ambient light conditions. A typical overhead projector uses a 150 watt bulb, while it is becoming desirable to use 400 watt (and higher) light sources in some integrated projectors under development. Along with higher intensity light sources comes more light and heat that needs to be controlled. The heat control problem is especially acute with respect to portable integrated projectors, which are often unplugged and packed into carrying bags or cases before they have had time to cool down after use (contrary to the manufacturer's instructions). If the cooling fan is turned off prematurely, enough heat can build up in a projector's lamp compartment (or plenum) to cause extremely hot air to exit the projector, perhaps sufficiently hot to melt or burn plastic and other projector components and to potentially cause injury and damage to nearby objects.
Exemplary integrated projectors are described in two patent applications owned by the assignee of the present invention. The first is U.S. patent application Ser. No. 08/623,729, entitled "COMPACT INTEGRATED LCD PROJECTOR", filed Mar. 29, 1996abandoned. The second is U.S. patent application Ser. No. 08/673,292, entitled "METHOD AND SYSTEM FOR THERMAL MANAGEMENT WITHIN A DISPLAY DEVICE", filed Jun. 28, 1996, issued as U.S. Pat. No. 5,692,821. Both of those applications are hereby incorporated by reference as background references.
In some projectors, the light source is located in a compartment or plenum that is open at both ends to permit air to circulate or to be drawn through the plenum, and a fan may be provided to force air through the plenum when the projector is connected in to a power source. The plenum is typically designed with louvered grills at each end to prevent undesirable amounts of light from escaping through the ends of the plenum, while permitting movement of cooling air through the plenum. Both the fan and the louvers may cause undesirable noises to be emitted by the projector when it is in use. In integrated projectors, the increased heat load generated by a higher-intensity light source requires the use of higher capacity cooling fans, which increase the amount of undesirable noise associated with the projector. Not only is the fan louder, but the noise of air rushing through the louvers may become unacceptably loud.
It is therefore desirable to provide a projector, such as a portable integrated projector, that contains a high-intensity light source that is sufficiently bright to project an image across a room from a small LCD panel under high ambient light conditions. It is further desirable to provide a light source assembly that does not permit objectionable amounts of light to escape through its ventilation channels, and that is not excessively noisy due to the operation of its fan and ventilation system. The desired light source assembly will preferably not release dangerously hot air during use or if it is unplugged immediately after use, and it will be energy efficient. Such a light source assembly is not known to exist in the prior art, and it is required for the development of the next generation of integrated projectors.